Centrifugal pump impeller

ABSTRACT

An impeller include a substantially cylindrical impeller body with an internal flow path connecting between an inlet opening through a first end surface and an outlet opening through a circumferential surface; and a balance weight embedded in the impeller body. The balance weight has a vertically-elongated shape in which its height in a cylindrical axis direction is larger than its thickness in a radial direction. The vertically-elongated balance weight is embedded in a circumferential section of the cylindrical impeller body.

TECHNICAL FIELD

A technique disclosed herein relates to a centrifugal pump impeller.

BACKGROUND ART

Conventionally, a centrifugal pump has been used for delivering, e.g., drainage. Among various impellers attached to the centrifugal pump, a non-clog impeller in which a flow path connecting between an inlet opening through a first end surface and an outlet opening through a circumferential surface is formed has been known as an impeller in which it is less likely to cause clogging of, e.g., drainage containing solid substances such as impurities (see, e.g., Patent Document 1).

The non-clog impeller has a single vane, and therefore is formed in non-symmetric shape about a rotation axis. Thus, in the impeller disclosed in Patent Document 1, a balance weight is provided in order to achieve static balance at rest and dynamic balance during rotation in air (hereinafter collectively referred to as “mechanical balance”), and to achieve balance during rotating the impeller in water (hydraulic balance). Specifically, in the impeller disclosed in Patent Document 1, a flat balance weight extending in a radial direction is attached to each of an upper surface of an upper flange section and a lower surface of a lower flange section which outwardly protrude in the radial direction around an entire circumference, with bolts.

CITATION LIST

-   PATENT DOCUMENT 1: Japanese Patent Publication No. 10-238495

SUMMARY OF THE INVENTION Technical Problem

Considering reduction in power of a submersible pump, the diameter of the impeller is desirably reduced. Meanwhile, if the diameter of particle passing through the impeller (the maximum diameter of particle which can pass through the flow path) is increased to enhance particle transmission, the diameter of the flow path formed in the impeller should be increased. Inventors of the present invention have recognized that, in order to realize both of the reduction in power of the submersible pump and the high particle transmission, the width of the radially-extending protrusion of the flange section of the impeller should be reduced. However, if the protrusion width of the flange section is reduced as described above, there is almost no lower surface region particularly in the lower flange section. As a result, the balance weight having a sufficient weight cannot be attached to such a section.

The centrifugal pump impeller disclosed herein is an advantageous impeller for achieving the mechanical balance and the hydraulic balance by attaching a balance weight to an impeller body, and realizing the enhancement of the particle transmission by increasing a flow path diameter and the reduction in power by reducing an impeller diameter.

Solution to the Problem

The inventors of the present invention have focused on a balance weight embedded in an impeller body. An example of a centrifugal pump impeller includes an impeller body having a substantially cylindrical shape with first and second end surfaces facing each other in a cylindrical axis direction, and with a circumferential surface interposed between the first and second end surfaces, and including an internal flow path which connects between an inlet opening through the first end surface and an outlet opening through the circumferential surface; and a balance weight embedded in the impeller body. The balance weight has a vertically-elongated shape in which its height in the cylindrical axis direction is larger than its thickness in a radial direction, and the vertically-elongated balance weight is embedded in a circumferential section of the cylindrical impeller body.

ADVANTAGES OF THE INVENTION

The vertically-elongated balance weight can be embedded in the circumferential section of the impeller body, which is relatively thin in the radial direction. The balance weight is embedded in the impeller body, and therefore it is not necessary to attach the balance weight to, e.g., a flange section. That is, by embedding the balance weight, the mechanical balance and the hydraulic balance can be achieved, and an increase in flow path diameter and a reduction in impeller diameter can be simultaneously realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a submersible pump including a centrifugal pump impeller which is illustrated as an example.

FIG. 2 is a perspective view of the impeller.

FIG. 3 is a front view of the impeller.

FIG. 4 is a bottom view of the impeller.

FIG. 5 is a V-V cross-sectional view of FIG. 4.

FIG. 6 is a plan view of an impeller body in a state in which a lid is removed.

FIG. 7 is a view illustrating a back-side surface of the lid.

FIG. 8 is a VIII-VIII cross-sectional view of FIG. 7.

FIG. 9 is an enlarged plan view around a boss section of the impeller body.

FIG. 10 is an enlarged cross-sectional view around the boss section of the impeller body.

FIG. 11 is a perspective view of an upper balance weight.

FIG. 12 is a perspective view of a lower balance weight.

DESCRIPTION OF EMBODIMENTS

An example of a centrifugal pump impeller includes an impeller body having a substantially cylindrical shape with first and second end surfaces facing each other in a cylindrical axis direction, and with a circumferential surface interposed between the first and second end surfaces, and including an internal flow path which connects between an inlet opening through the first end surface and an outlet opening through the circumferential surface; and a balance weight embedded in the impeller body. The balance weight has a vertically-elongated shape in which its height in the cylindrical axis direction is larger than its thickness in a radial direction, and the vertically-elongated balance weight is embedded in a circumferential section of the cylindrical impeller body.

According to the foregoing configuration, the balance weight has the vertically-elongated shape. This allows the balance weight to be embedded in the circumferential section of the impeller body, which is relatively thin in the radial direction. The balance weight is embedded in the impeller body, and therefore it is not necessary to attach the balance weight to, e.g., a flange section. Thus, an increase in flow path diameter and a reduction in impeller diameter can be simultaneously realized.

One end section of the impeller body may serve as a relatively-thin wear ring section provided so as to surround the inlet, and the balance weight may be embedded in the wear ring section.

The flange section of the impeller body is positioned inside a volute chamber of a casing, and therefore the balance weight can be attached to, e.g., an outer circumferential surface of the flange section. On the other hand, the wear ring section faces a liner ring of the casing with a slight clearance therebetween, and therefore the balance weight cannot be attached to, e.g., an outer circumferential surface of the wear ring section. The configuration in which the balance weight is embedded in the impeller body is advantageous particularly when embedding the balance weight in the wear ring section.

A lower end surface of the balance weight embedded in the wear ring section may be exposed in the first end surface of the impeller body, and a though-hole passing through the balance weight in a thickness direction or a notch recessed in the lower end surface may be formed in the balance weight. The impeller body includes a retaining section of the balance weight, which is formed by filling the through-hole or the notch of the balance weight with resin when forming the impeller body by molding.

There is a possibility that the balance weight is disengaged during use of the impeller. However, the lower end surface of the balance weight is exposed in the first end surface of the impeller body, and therefore the retaining section reduces or prevents such disengagement. In addition, a simple technique is used, in which the through-hole or the notch is provided in the balance weight to form the impeller body by molding. Thus, the disengagement of the balance weight can be reduced or prevented.

A plurality of positioning holes may be formed in the balance weight. A positioning pin for positioning the balance weight in a predetermined section inside a mold when forming the impeller body by molding may be inserted into each of the positioning holes.

In such a manner, the balance weight is accurately positioned in the predetermined section inside the mold, thereby ensuring the balance weight embedded in the circumferential section of the impeller body.

An embodiment of the impeller will be described below with reference to the drawings. Note that the embodiment below has been set forth merely for purposes of a preferred example in nature. FIG. 1 illustrates a submersible pump 1 including an impeller which is illustrated as an example. The submersible pump 1 includes a pump section 21 with an impeller 6, and a motor section 22 with a motor 3 for driving the impeller 6. In the submersible pump 1, the pump section 21 is arranged below an oil casing 23, and the motor section 22 is arranged above the oil casing 23. That is, the pump section 21 and the motor section 22 are arranged one above the other. The submersible pump 1 is a lightweight pump in which a head cover 34 and a pump casing 4 which will be described later are made of predetermined resin material.

The motor section 22 includes the motor 3 with a stator 31 and a rotor 32; a stator casing 33 covering the stator 31 of the motor 3; and the head cover 34 attached to an upper end of the stator casing 33. A rotating shaft 35 of the motor 3 vertically extends.

The stator casing 33 is formed in substantially cylindrical shape with upper and lower openings. The upper opening of the stator casing 33 is closed with a motor cover 36, and a bearing 35 a rotatably supporting an upper end section of the rotating shaft 35 is provided on a lower surface of the motor cover 36.

The head cover 34 is attached to the upper end of the stator casing 33. The head cover 34 has an upper wall and a circumferential wall which downwardly extends from a circumferential section of the upper wall, and which is fixed to an upper end section of the stator casing 33. In addition, the head cover 34 has an inverted U-shaped cross section. Thus, the head cover 34 and the motor cover 36 defines a housing space 34 a in which various electric components are housed. A cable boot into which a power feeding cable for feeding power to the motor 3 is inserted is attached so as to pass through the upper wall of the head cover 34, and a handle 34 b is attached to a center section of an upper surface of the upper wall. The head cover 34 is fixed to the oil casing 23 with a plurality of bolts 37 (only one bolt is illustrated in the figure) arranged at predetermined interval in the circumferential direction. That is, the bolt 37 inserted into a through-hole formed in a circumferential section of the head cover 34 passes through the motor cover 36. Then, the bolt 37 downwardly extends along an inner circumferential surface of the stator casing 33, and is screwed into a circumferential section of the oil casing 23. In such a manner, in the submersible pump 1, the long vertically-extending bolt 37 fixes the head cover 34, the stator casing 33, and the motor cover 36 to the oil casing 23 at one time. Such a configuration allows reduction in the number of components and the number of assembly steps of the submersible pump 1.

The oil casing 23 is attached to a lower end of the stator casing 33, and the lower opening of the stator casing 33 is closed with the oil casing 23. The pump casing 4 is attached to a lower side of the oil casing 23, and therefore the oil casing 23 and the pump casing 4 define an oil chamber 53 filled with lubricating oil. A through-hole into which the rotating shaft 35 of the motor 3 is inserted is formed in the oil casing 23, and a bearing 35 b rotatably supporting a middle section of the rotating shaft 35 is attached to an upper surface of the oil casing 23. In the oil chamber 53 defined by the oil casing 23 and the pump casing 4, the rotating shaft 35 is sealed by a mechanical seal 51, and a circular wall 52 is provided, which surround a substantially entire outer circumferential section of the mechanical seal 51.

The pump section 21 includes the impeller 6 attached to a lower end of the rotating shaft 35 of the motor 3, and the pump casing 4. The submersible pump 1 is a centrifugal pump. A first pump casing 41 on an upper side, which defines the oil chamber 53 together with the oil casing 23, and a second pump casing 42 on a lower side are integrated by welding, thereby forming the pump casing 4. The first pump casing 41 and the second pump casing 42 are integrated by welding as described above, and therefore a flange is not required, which is required, e.g., when integrating two pump casings with a bolt-nut fastening means. Consequently, the size of the submersible pump 1 is reduced.

A through-hole into which the rotating shaft 35 is inserted is formed in an upper section of the pump casing 4, and a volute chamber 43 in which the impeller 6 is housed is formed inside the pump casing 4. The pump casing 4 has a lower opening, and a liner ring 44 with an opening 44 a, which supports a wear ring section 692 which is a lower end section of the impeller 6 is attached to such an opening. A discharge section 45 which laterally protrudes, and which is upwardly curved is integrally formed with a side section of the pump casing 4. The discharge section 45 communicates with the volute chamber 43, and has a discharge port 45 a with an upper opening. The discharge port 45 a is connected to an outlet pipe which is not shown in the figure. Four downwardly-extending legs 46 (only three legs 46 are illustrated in FIG. 1) are arranged in a lower section of the pump casing 4 in a predetermined pattern, and lower ends of the legs 46 are attached and fixed to a seat 7. The seat 7 includes a body section 71 made of synthetic resin; and a cover 72 which covers a lower side of the body section 71, and which is made of rubber. Inserting sections 73 into which the lower ends of the legs 46 are inserted, and in which the lower ends of the legs 46 are fastened with screws are integrally formed with the body section 71 so as to upwardly protrude. A damping rubber member or damping steel plate 74 is interposed between a lower surface of the leg 46 and the inserting section 73. The seat 7 functions to reduce or prevent displacement of a position where the submersible pump 1 is arranged due to the cover 72, and to control vibration by the damping rubber member or damping steel plate 74 when driving the submersible pump 1.

As illustrated in FIGS. 2-5, the impeller 6 is a non-clog impeller having a substantially cylindrical shape, and is fixed to the lower end of the rotating shaft 35 so that a cylindrical axis of the impeller 6 is coaxial to the rotating shaft 35 (see FIG. 1). The impeller 6 includes an impeller body 61, and a lid 62 attached to an upper end surface of the impeller body 61. In addition, in order to achieve mechanical and hydraulic balance, the impeller 6 also includes an upper balance weight 63 and a lower balance weight 64. Although details will be described later, the upper balance weight 63 is arranged and fixed between the impeller body 61 and the lid 62, and the lower balance weight 64 is embedded in the wear ring section 692 of the impeller body 61 as illustrated in FIG. 5.

The impeller body 61 has a substantially cylindrical shape. An inlet 601 opening at the bottom of the impeller body 61 is formed in a lower end surface of the impeller body 61, and an outlet 602 opening through a side of the impeller body 61 is formed in a predetermined section of a circumferential surface of the impeller body 61. An internal flow path 603 extending in the cylindrical axis direction is formed inside the impeller 6, and the internal flow path 603 connects between the inlet 601 and the outlet 602. An external flow path 604 inwardly recessed in the radial direction is formed in an outer circumferential surface of the impeller body 61. The external flow path 604 is not a flow path extending in the cylindrical axis direction, and the center of the flow path is positioned on a plane perpendicular to the cylindrical axis of the impeller body 61. The external flow path 604 reaches a downstream side of the internal flow path 603 at the outlet 602, and extends across a substantially entire perimeter of the impeller 6. The external flow path 604 is defined by a vane 605. The vane 605 is a so-called “single radial-flow vane (centrifugal vane), and the centrifugal vane 605 increases the pressure of water in the external flow path 604, and then discharges such water to an outer circumferential side (outer side in the radial direction). A first flange section 681 outwardly protruding in the radial direction around an entire circumference is formed above the external flow path 604 of the impeller body 61. In addition, a second flange section 682 outwardly protruding in the radial direction around the entire circumference is also formed below the external flow path 604. The second flange section 682 horizontally divides the impeller 6 into a lower section where the inlet 601 is formed, and an upper section where the outlet 602 is formed. That is, the impeller 6 is a closed-type impeller in which the second flange section 682 divides between the inlet 601 and the outlet 602.

A shaft support section 691 is formed so as to upwardly protrude in the center of the upper end surface of the impeller body 61, which is above the first flange section 681. The shaft support section 691 is made of predetermined metal material, and is provided with an attachment hole into which the rotating shaft 35 of the motor 3 is inserted to be fixed. In addition, the downwardly-protruding wear ring section 692 inserted into the opening 44 a of the pump casing 4 is formed below the second flange section 682 of the impeller body 61.

In order to reduce power of the submersible pump 1, the first and second flange sections 681 and 682 are set to a smaller diameter so that the diameter of the impeller body 61 becomes as small as possible. Thus, as illustrated in FIGS. 3 and 5, the impeller body 61 is designed with almost no step between the second flange section 682 and the wear ring section 692. The diameters of the first and second flange sections 681 and 682 may be further reduced in order to, e.g., eliminate such a step. Conversely, the diameter of the wear ring section 692 is increased so that the diameter of the inlet 601 is increased, thereby eliminating the step between the second flange section 682 and the wear ring section 692.

The impeller body 61 is made of synthetic resin. As illustrated in FIGS. 5 and 6, a recessed section 611 recessed in the cylindrical axis direction in the upper end surface of the impeller body 61 is formed in order to reduce or prevent shrinkage caused when forming the impeller due to the substantially constant thickness of the impeller. As illustrated in FIG. 6, the recessed section 611 extends substantially three-fourths of the entire perimeter from an opening side of the outlet 602 (upper side as viewed in FIG. 6), in the counterclockwise and circumferential directions. In addition, as illustrated in FIG. 5, the recessed section 611 is formed so that the depth is relatively shallow on the opening side of the outlet 602 (right side as viewed in FIG. 5), and the depth is relatively deep on a side opposite to the opening side of the outlet 602 (left side as viewed in FIG. 5).

Reinforcement ribs 612 extending in the radial direction, and connecting between the shaft support section 691 and a circumferential section of the impeller body 61 are formed in an upper end section of the impeller body 61. In the present embodiment, in the impeller body 61 illustrated in FIG. 6, three reinforcement ribs 612 are formed at predetermined angles in an upper half region corresponding to the opening side of the outlet 602, and a single reinforcement rib 612 is formed in a lower half region corresponding to the side opposite to the opening side of the outlet 602. Three of the four reinforcement ribs 612 are arranged inside the recessed section 611. As illustrated in, e.g., FIG. 10, the three reinforcement ribs 612 arranged on the opening side of the outlet 602 are also used as a mounting section on which the upper balance weight 63 is mounted. That is, an upper end surface of each of the reinforcement ribs 612 serves as a mounting surface 614 on which the upper balance weight 63 is mounted. Further, a boss section 613 for fixing the upper balance weight 63 is formed in the substantially center of the reinforcement rib 612 in the radial direction.

As illustrated in FIGS. 9 and 10, the boss section 613 is formed in circular shape as viewed in plan, which has a diameter larger than the width of the reinforcement rib 612. An upwardly-opening pinhole 615 which extends in the cylindrical axis direction is formed in the center of the boss section 613. In an outer circumferential surface of the boss section 613, three protrusions 616 outwardly protruding in the radial direction are integrally formed with the boss section 613 at equal interval in the circumferential direction.

As illustrated in FIG. 11, the upper balance weight 63 made of predetermined metal material is formed in substantially fan-like shape by cutting a section corresponding to a predetermined angular range from an annular disk-like member having a predetermined thickness. The upper balance weight 63 has a flattened shape in which the width of the upper balance weight 63 in the radial direction is larger than the thickness of the upper balance weight 63 in the cylindrical axis direction (vertical direction). As illustrated in FIG. 6, the upper balance weight 63 is arranged between the shaft support section 691 and the circumferential section of the impeller body 61. Thus, the inner diameter of the upper balance weight 63 is set so as to be larger than the diameter of the shaft support section 691, and the outer diameter of the upper balance weight 63 is set so as to be smaller than the diameter of the circumferential section of the impeller body 61. The shape of the upper balance weight 63 is not limited, and may be suitably set so that a required weight can be ensured under a condition where the upper balance weight 63 is arranged between the impeller body 61 and the lid 62. In the upper balance weight 63, three holes 631 passing through the upper balance weight 63 in a thickness direction are formed corresponding to the three boss sections 613. Each of such holes is a fitting hole 631 fitted onto the boss section 613. As hypothetically illustrated in FIG. 9, the diameter of such a hole is set so as to be larger than that of the boss section 613, and to be smaller than that of a circle defined by connecting tip ends of the protrusions 616.

As illustrated in enlarged views of FIGS. 9 and 10, the upper balance weight 63 is mounted on the mounting surface 614 of the reinforcement rib 612 so that each of the fitting holes 631 is fitted onto the boss section 613. Thus, the upper balance weight 63 is positioned in a predetermined section of the upper end surface of the impeller body 61 on the opening side of the outlet 602. The fitting hole 631 of the upper balance weight 63 is set so as to have the diameter larger than that of the boss section 613, and smaller than that of the circle defined by connecting the tip ends of the protrusions 616. Thus, a part of the protrusions 616 is pressed against the boss section 613, thereby fitting the fitting hole onto the boss section 613. This reduces the rattling of the upper balance weight 63.

As illustrated in FIGS. 7 and 8, the lid 62 has a circular disk-like shape, and a through-hole 621 into which the shaft support section 691 of the impeller body 61 is inserted is formed in the center of the lid 62. The lid 62 is made of synthetic rein. A front-side surface of the lid 62 is flat. On each of a side corresponding to the opening of the outlet 602 and its opposite side with respect to the cylindrical axis in the circumferential section of the lid 62, two engagement claws 622 are integrally formed with the lid 62 at predetermined interval in the circumferential direction. The engagement claw 622 is a claw to be engaged with an engagement groove 683 formed at a circumference of the upper end section of the impeller body 61, and the engagement claw 622 and the engagement groove 683 serve as an engagement means for attaching and fixing the lid 62 to the impeller body 61.

In positions of a back-side surface of the lid 62 corresponding to the boss sections 613 of the impeller body 61, three pins 623 are formed so as to protrude from the back-side surface. As illustrated in FIG. 10, when attaching the lid 62 to the impeller body 61, each of the pins 623 is fitted into the pinhole 615 formed in the boss section 613. In addition to the engagement of the engagement claw 622 with the engagement groove 683, the fitting of the pin 623 into the pinhole 615 allows the lid 62 to be more stably attached and fixed to the impeller body 61. Holding sections 624 for holding the upper balance weight 63 are further formed so as to protrude from the back-side surface of the lid 62. The holding section 624 is formed in circular shape so as to surround the pin 623. As illustrated in FIG. 10, when attaching and fixing the lid 62 to the impeller body 61, a lower surface of the holding section 624 downwardly presses against an upper surface of the upper balance weight 63 around the boss section 613. Thus, the upper balance weight 63 is sandwiched between the lid 62 and the impeller body 61.

In the lid 62, two through-holes 625 are formed on each of the opening side of the outlet 602 and its opposite side. Such through-holes are air vent holes 625 through which air is vented from the recessed section 611 of the impeller body 61 to fill the recessed section 611 with water. Air vent holes may be formed in the upper balance weight 63. In such a case, such air vent holes are desirably formed in the same positions as those of the air vent holes 625 formed in the lid 62. The air vent holes 625 are provided in the lid 62 to fill the recessed section 611 with water as described above. Thus, this reduces or prevents a loss of mechanical balance of the impeller 6 due to remaining air in the recessed section 611, and reduces occurrence of vibration when driving the impeller 6.

As illustrated in FIGS. 3 and 4, the lower balance weight 64 is embedded in the wear ring section 692 on the opening side of the outlet 602 of the impeller body 61. As illustrated in, e.g., FIG. 12, the lower balance weight 64 made of predetermined metal material is a plate curved in arc, and has a vertically-elongated shape in which a height in the cylindrical axis direction is larger than a thickness in the radial direction. As illustrated in FIG. 4, the lower balance weight 64 is embedded in the wear ring section 692 so that a lower end surface of the lower balance weight 64 is exposed in the lower end surface of the impeller body 61. Two through-holes 641 are formed in predetermined positions of the lower balance weight 64, and each through-hole 641 serves as a positioning hole into which a positioning pin 8 of a mold is inserted. A notch 642 is formed in a center section of a lower end of the lower balance weight 64. When forming the impeller body 61 by molding, a section corresponding to the notch 642 is filled with resin, and therefore a retaining section 694 is formed, which crosses the lower balance weight 64 in the thickness direction as illustrated in FIG. 4.

Next, a manufacturing process of the impeller body 61 will be briefly described. First, the shaft support section 691 and the lower balance weight 64 are arranged in predetermined positions inside the mold (not shown in the figure). In such a state, a position of the lower balance weight 64 in the circumferential direction, and an inclination of the lower balance weight 64 are determined by the two positioning pins 8 as illustrated in FIG. 12. The positioning pin 8 includes a small-diameter section 81 on a tip end side, and a large-diameter section 82 on a base end side. A position of the lower balance weight 64 in the radial direction is also determined by a position of a step defined by such sections having the different diameters. In such a manner, the lower balance weight 64 can be accurately positioned in a predetermined section inside the mold, thereby ensuring the lower balance weight 64 embedded in the thin wear ring section 692 of the impeller body 61.

Then, the impeller body 61 is formed by a well-known resin molding. As illustrated in FIGS. 2 and 3, holes 693 are formed in the wear ring section 692 of the molded impeller body 61 by the positioning pins 8.

Next, the separately-prepared upper balance weight 63 is attached to the upper end surface of the molded impeller body 61. As described above, in the upper balance weight 63, the fitting hole 631 of the upper balance weight 63 is fitted onto the boss section 613 with the protrusions 616 of the boss section 613 being pressed against the fitting hole 631.

Subsequently, the separately-molded lid 62 is attached to the impeller body 61. In such a state, the pin 623 of the lid 62 is fitted into the pinhole 615 of the impeller body 61, and the engagement claw 622 of the lid 62 is elastically deformed to be engaged with the engagement groove 683 of the impeller body 61. When attaching and fixing the lid 62 to the impeller body 61, the holding sections 624 of the lid 62 press against the upper balance weight 63. Thus, attachment of the upper balance weight 63 to the impeller body 61 is completed.

As described above, in the impeller 6 having the foregoing configuration, the fastening means such as bolts is not used to fix the lid 62 to the impeller body 61, and the engagement claws 622 are engaged with the engagement grooves 683 to attach and fix the lid 62 to the impeller body 61. Thus, tools etc. are not required for the assembly process, and the assembly of the impeller 6 is simplified. In addition, when attaching the lid 62 to the impeller body 61, the upper balance weight 63 is fixed to the impeller body 61.

Consequently, the assembly process of the impeller 6 is further facilitated.

The engagement claws 622 are provided in the lid 62, and the engagement grooves 683 opening toward outside are provided in the circumferential section of the impeller body 61. Thus, in a state in which the lid 62 is attached to the impeller body 61, the engagement sections are not protrude from the front-side surface of the lid 62, thereby ensuring the flat surface at the upper end of the impeller 6. This is advantageous to reduce a power loss. Note that engagement grooves may be provided in the lid 62, and engagement claws may be provided in the impeller body 61. The engagement section where the lid 62 is engaged with the impeller body 61 is not limited to the combination of the engagement claw 622 and the engagement groove 683, and any configuration may be employed.

The circumferential section of the lid 62 is fixed to the impeller body 61 by the engagement claws 622 and the engagement grooves 683, and the pins 623 provided in the lid 62 are fitted into the pinholes 615 of the impeller body 61. Thus, an inner section of the lid 62 in the radial direction can be fixed to the impeller body 61. Consequently, the inner section of the lid 62 in the radial direction is not apart from the impeller body 61.

The fitting hole 631 of the upper balance weight 63 is fitted onto the boss section 613 of the impeller body 61. Thus, the upper balance weight 63 can be correctly positioned on the predetermined section of the impeller body 61, and the occurrence of the rattling of the upper balance weight 63 can be reduced or prevented.

The reinforcement rib 612 improves the strength of the impeller body 61 itself. In addition, the upper balance weight 63 and the boss section 613 used for the fixing of the lid are integrally formed with the reinforcement rib 612, thereby improving the stiffness of the boss section 613. This is advantageous to more stably fix the upper balance weight 63 and the lid 62 to the impeller body 61.

Unlike the upper balance weight 63, the lower balance weight 64 has the vertically-elongated shape, thereby embedding the lower balance weight 64 in the wear ring section 692 which is thin in the radial direction. The lower balance weight 64 is embedded in the impeller body 61, and therefore it is not necessary to attach the balance weight to the second flange section 682. This allows the diameter of the inlet 601 of the impeller 6 to be as large as possible, thereby ensuring predetermined substance passage properties. In addition, the diameters of the first and second flange sections 681 and 682 become as small as possible in order to reduce the diameter of the impeller 6, thereby reducing the power of the submersible pump 1.

The lower end surface of the lower balance weight 64 embedded in the wear ring section 692 is exposed in the lower end surface of the impeller body 61, and therefore there is a possibility that the lower balance weight 64 is disengaged during use of the impeller 6. However, the retaining section 694 is configured by forming the notch 642 at the lower end of the lower balance weight 64, thereby reducing or preventing the disengagement of the lower balance weight 64. In the present embodiment, the retaining section 694 is configured by forming the notch 642 at the lower end of the lower balance weight 64. However, a through-hole passing through the lower balance weight 64 in the thickness direction may be formed in, e.g., a middle section of the lower balance weight 64 in the height direction, thereby forming a resin retaining section crossing the lower balance weight 64 in the thickness direction. Alternatively, the entire lower balance weight 64 may be embedded in the impeller body 61, and therefore the lower end of the lower balance weight 64 may not be exposed. In such a case, the retaining section is not required.

In the foregoing embodiment, the lower balance weight 64 is embedded in the wear ring section 692. However, e.g., if the height of the lower balance weight 64 is increased under a condition where the required weight is ensured, an upper end section of the lower balance weight 64 may be positioned corresponding to the second flange section 682.

The lower balance weight 64 is not limited to the configuration in which the lower balance weight 64 is embedded in the wear ring section 692, and the lower balance weight 64 may be embedded in any parts of the circumferential section of the impeller body 61.

The impeller is not limited to the impeller made of synthetic resin.

DESCRIPTION OF REFERENCE CHARACTERS

-   1 Submersible Pump -   6 Impeller -   601 Inlet -   602 Outlet -   603 Internal Flow Path -   61 Impeller Body -   64 Lower Balance Weight -   641 Positioning Hole -   642 Notch -   692 Wear Ring Section -   694 Retaining Section -   8 Positioning Pin 

1. A centrifugal pump impeller, comprising: an impeller body having a substantially cylindrical shape with first and second end surfaces facing each other in a cylindrical axis direction, and with a circumferential surface interposed between the first and second end surfaces, and including an internal flow path which connects between an inlet opening through the first end surface and an outlet opening through the circumferential surface; and a balance weight embedded in the impeller body, wherein the balance weight has a vertically-elongated shape in which its height in the cylindrical axis direction is larger than its thickness in a radial direction, and the vertically-elongated balance weight is embedded in a circumferential section of the cylindrical impeller body.
 2. The centrifugal pump impeller of claim 1, wherein one end section of the impeller body serves as a relatively-thin wear ring section provided so as to surround the inlet; and the balance weight is embedded in the wear ring section.
 3. The centrifugal pump impeller of claim 2, wherein a lower end surface of the balance weight embedded in the wear ring section is exposed in the first end surface of the impeller body, and a though-hole passing through the balance weight in a thickness direction or a notch recessed in the lower end surface is formed in the balance weight; and the impeller body includes a retaining section of the balance weight, which is formed by filling the through-hole or the notch of the balance weight with resin when forming the impeller body by molding.
 4. The centrifugal pump impeller of claim 1, wherein a plurality of positioning holes are formed in the balance weight; and a positioning pin for positioning the balance weight in a predetermined section inside a mold when forming the impeller body by molding is inserted into each of the positioning holes. 